Historically, computer systems have been designed and produced without careful considerations for video and to a lesser extent audio capabilities. Many systems have been produced that add video capability to the computer system by colour keying and analogue multiplexing of the computer's graphics output. For example U.S. Pat. No. 5,027,212. Such systems generally involve multiple frame buffers holding video and graphics data separately. More recently a unified approach based on a single frame buffer of the type described in our International Patent Application No. PCT GB9202164 (published as PCT Application No. WO 93/10518 on May 27, 1993, and filed as U.S. Ser. No. 08/244,399 on Jul. 21, 1994) has been adopted. This approach treats video and graphics in exactly the same way. The single frame buffers can be based on either triple port memories or time multiplexing of video and graphics data on a common bus using suitable rate buffering and arbitration as described in the above numbered International patent application.
These techniques can be or have been used to integrate video into a computer display system. However, to date, such integration has been carried out within the constraints of the available personal computers and workstations. This has meant that such systems are costly and bulky and have limited expandability.